1. Field of the Invention
The present invention is broadly directed to the storage of core assemblies from a nuclear reactor. In a more particular aspect, it is directed to the storage of core assemblies from a liquid metal-cooled reactor of the loop or pool type. In a pool type reactor the nuclear reactor core and various auxiliary equipment such as intermediate heat exchangers, pumps and the like, are all immersed in a pool of liquid metal coolant and contained within a sealed vessel as opposed to a loop type of reactor wherein only the reactor core is contained within the pool of liquid sodium and the pumps and heat exchanger are located externally of the vessel containing the sodium and core.
2. Description of the Prior Art
Most, if not all, nuclear powered facilities for the generation of electrical power include provisions for onsite temporary storage of spent nuclear fuel assemblies. The reason for such temporary storage is to allow the spent fuel assemblies to decay to a temperature and radiation level that will permit their being placed in canisters for shipment to a permanent disposal or fuel reprocessing site. In the case of water-cooled reactors, the fuel assemblies are typically immersed in a large pool of water. Generally, pumps and heat exchangers are provided to cool the water as required.
Such a storage system, while satisfactory for water-cooled reactors, presents several disadvantages when utilized with a liquid-metal cooled reactor. Obviously, water cannot be used as the cooling medium since the fuel assemblies would have residual alkali metal such a sodium contained thereon and sodium is highly reactive with water. In addition, if sodium is used as the coolant in a storage pool, the problems of temperature control are substantially compounded. Specifically, there must also be means included for maintaining the temperature of the sodium or liquid metal above its melting point when there were none or only a few heat generating core assemblies contained therein. Conversely, if the pool of liquid metal were filled to capacity with, for example, spent fuel elements, then it might be necessary to provide some means for dissipating the heat that they would generate. Further, in many instances it may be required to provide surge tanks to compensate for the differences in volume in the storage vessel resulting from changes in the number of core assemblies contained therein. Still further, a high temperature liquid metal which is highly reactive is more difficult to contain and circulate than, for example, water. Another disadvantage of using a pool of liquid metal for storage of core assemblies is the large inventory of sodium required. Still another disadvantage is the necessity of an auxiliary power supply to maintain safe operation of the storage system in the event of a general power failure.